Setting up Auto Scaling Group

[Rumman]

We have the following questions

Category: CSAA – Design Resilient Architectures

You are a Solutions Architect for a major TV network. They have a web application running on eight Amazon T3 EC2 instances, consuming about 55% of resources on each instance. You are using Auto Scaling to make sure that eight instances are running at all times. The number of requests that these application processes are consistent and do not experience spikes. Your manager instructed you to ensure the high availability of this web application at all times to avoid any loss of revenue. You want the load to be distributed evenly between all instances. You also want to use the same Amazon Machine Image (AMI) for all EC2 instances.

How will you be able to achieve this?

and the answer is given:

Deploy four EC2 instances with Auto Scaling in one Availability Zone and four in another availability zone in the same region behind an Amazon Elastic Load Balancer.

I am wondering how this is the correct answer? Because if one az goes down we will have only four instances. Rather isn’t we need to deploy

Deploy EC2 instances with Auto Scaling in three Availability Zone and four in each availability zone behind an Amazon Elastic Load Balancer;

so in that case, even one goes down the other two az can maintain at least 8 instances all the time.

[Gerome-TutorialsDojo]

Hello Rumman,

Thanks for sharing your thoughts.

Yes, I understand using Auto Scaling in three AZ is a possible option but that approach is not cost-efficient because you’d have a total of 12 instances running. Also, the requirement in the scenario is highly available (HA) architecture and not both HA and fault tolerance.

Deploying the instances in two Availability Zones would ensure the application is highly available. When the first AZ goes down, the second AZ will only have an initial 4 EC2 instances. This will eventually be scaled up to 8 instances since the solution is using Auto Scaling.

Based on the provided explanation in the scenario, were you able to view the reference links as well? You’ll see there a link to the AWS documentation where we based this scenario. Kindly check it and if you’re still in doubt, feel free to let me know.

Let us know if you need further assistance. The Tutorials Dojo team is dedicated to helping you pass your AWS exam on your first try!

Regards,

Gerome @ Tutorials Dojo